This invention relates to a device for protecting human eyes, electro-optical sensors and sensitive materials against excessive optical power densities and energy densities.
Because of their high inherent sensitivity, eyes and electronic sensors are endangered by excessive optical power densities and energy densities. As protective measures, the state of the art provides diverse passive and active measures, such as interference filters, holographic filters, mechanical locks and self-actuating optical switches. These measures, however, frequently provide insufficient protection, either because they are effective only in a limited spectral region, or because the sensitivity of the sensor is impaired. Moreover, in some cases, after a threat posed by high energy radiation has subsided, the protective device does not revert appropriately to normal operation, or--particularly in the case of laser pulses--the reaction is too slow. Another problem of the state of the art is the high technical expenditures--mainly weight and volume--in the case of many common protective measures.
It is therefore an object of the invention to provide a protective device of the above-mentioned type which ensures reliable protection over a large spectral region with the shortest time delay, and which reacts in a coordinated manner with respect to time as well as with respect to the power densities and energy densities.
These and other objects and advantages are achieved by the protective device according to the invention, in which the incidence of a high energy light beam on the element to be protected is detected by a warning sensor. The warning sensor triggers a light source to provide a light beam which, with minimal delay, causes a diminution in the transmissivity of a protective element interposed in the beam path of the high intensity light beam. Due to the extremely rapid response time of these components, the protective response of the invention adapts almost immediately to changes in the intensity of an incident high energy light beam, thereby providing necessary protection and prompt return to normal transmissivity upon termination of the potentially damaging radiation.
The invention is thus based on the principle that the optical transmission properties of certain materials are altered by the incidence of high energy light, (preferably laser light), and that therefore their transition from a maximal absorption as well as the inverse effect can be utilized. Numerous materials exhibit such characteristics that can be utilized in this manner, of which the following are but a few examples:
Absorption of dyes, PA1 intensity-dependent transmission action of semiconductor substances PA1 production of plasma PA1 self-defocussing PA1 total internal reflection PA1 induced scattering
The decisive advantage of all these effects is their short reaction time, typically less than a nanosecond, which is absolutely necessary if they are to be used for protective purposes, particularly for protection against laser pulses. It is known that the triggering of these effects requires very high power densities in the protective medium, and to some extent a defined excitation wavelength.
In order for the interference radiation to trigger the protection of the sensor itself, the protective medium must be arranged in the focal range, which in turn, requires an additional intermediate projection. In addition, it should be noted that in prior art devices, even under these conditions, the switching and diminishing effect frequently did not occur before threshold values were reached which were above the danger limit of the used sensor. Therefore, all the protective measures of the state of the art must be considered to be unsatisfactory.
However, an optimization is achieved by utilization of the above-mentioned effects in the protective device according to the invention because they are triggered in a targeted and requirement-oriented manner by the light of an external radiation source, preferably by a laser. The power density, the wavelength and the time response of the radiation are therefore optimally adapted to the requirements by the selection of the light source, its control and by the coupling-in of its radiation energy.